Disk drives are digital data storage devices which can enable a host device to store and retrieve large amounts of data in a fast and efficient manner. A typical disk drive includes a plurality of magnetic recording disks which are mounted to a rotatable hub of a spindle motor and rotated at a high speed. An array of read/write transducers is disposed adjacent surfaces of the disks to transfer data between the disks and the host device. The transducers can be radially positioned over the disks by a rotary actuator and a servo system.
A plurality of nominally concentric tracks can be defined on each disk surface. As understood by those skilled in the art, a preamp and driver circuit generates write currents that are used by a first transducer to selectively magnetize the tracks during a data write command. A secondary transducer, generally proximate to the first transducer, amplifies read signals detected by the transducer from the selective magnetization of the tracks during a data read command. Under certain configurations, the first and second transducers can be fashioned to be one in the same. A read/write channel and interface circuit are connected to the preamp and driver circuit to transfer the data between the disks and the host device.
Each transducer (or transducer pair) is connected to a structure referred to as a “slider.” The slider is mounted on a spring-loaded flexible beam structure that can cause the slider with the connected transducer to press against a disk surface when the disk is stationary. When the disk spins up to operating speed, the high rotational speed causes air to flow under the slider thereby generating a fluid or hydrodynamic bearing, commonly referred to as an “air bearing” by those skilled in the art. The purpose of the air bearing is to provide adequate and appropriate force on the transducer-bearing slider so that a threshold separation is maintained between the transducer and the disk. Thus, a transducer floats over the surface of a spinning disk without physically touching the disk. The space between a transducer and a spinning disk (i.e., the transducer-to-disk clearance) is referred to as the “head/disk clearance” or just “clearance.” Clearance is an important parameter for operation of a disk drive. If clearance is too large, a transducer cannot properly read and write a disk. If clearance is too small, there is chance that the transducer will crash into the spinning disk and cause physical damage to either or both the transducer and disk (referred to as “disk crash”). The operating clearance is also important even in the intermediate case(s) where the head has neither excessively large clearance nor unacceptably small clearance. The significance of this last regime is an outcome of the fact that optimal reading and writing performance may be carefully tuned under a fairly small range of allowable clearance values.
The altitude at which a disk drive operates influences clearance. At high altitudes, the reduced air pressure generally diminishes the ability of the air bearing to maintain proper clearance, which can cause a disk crash. Unfortunately, conventional disk drives are not configured to detect operating altitude. Although numerous altitude detection technologies exist that utilize pressure transducers for barometric estimation of altitude, cost, measurement sensitivity, accuracy and packaging concerns have prevented incorporation into disk drives here-to-date. As such, a need exists for an economical, yet reliable, way to detect operating altitudes of disk drives.